Moving forward is a difficult thing... Every step you take is a step you might find yourself tempted to reget at a later point. Unless you're resolved to accept the consequences, it's often more comfortable to stay right where you are.

But dwelling on the past can easily hurt both oneself and others.

I like your way of thinking about it. Clearing a level is not something one wants to take back, right? Wherever the path leads, a higher level is a good thing to reach.